This invention relates to a screen printing machine employing vacuum pallets to support and register the article to be printed upon. This invention relates especially to a means for supplying a vacuum to said pallets, and to a vacuum pallet itself.
Silk screen printing is a well-known technique for producing articles that have decorative patterns or words printed thereon. Such printing has been used for a variety of articles, such as T-shirts, socks, posters and the like. A pallet is commonly used to support and position the article for printing. When a T-shirt is decorated, for example, it is usually slipped over a pallet which is then positioned under the printing head. In this way, article handling is facilitated and a flat printing surface is assured.
In some applications, e.g., when printing large posters, a different method of supporting and registering the article is needed. One such method is the use of a vacuum pallet; this is a pallet having a vacuum chamber in its interior, at least one port through which the chamber may be evacuated, and small holes through the article-receiving surface so that the vacuum will hold the article in place on the pallet. A vacuum pallet, and associated apparatus, is described in U.S. Pat. No. 3,763,776, the disclosure of which is incorporated herein by reference.
Because each pallet must be mobile, it is common practice to supply each vacuum pallet with its own small motor to generate a vacuum. This arrangement has several disadvantages. A great deal of noise is generated, since a large number of pallets having motors is commonly needed. The weight of each pallet is greatly increased by the motor attached thereto. Furthermore, there are severe practical limitations on motor size, and thus on vacuum power, because large motors are not suitable for mobile pallets. In addition, a great deal of vibration is produced by the motors, and such vibration may affect the steadiness of the pallet during printing operations.